It is known that resinous materials can be synthesized by the reaction of an aromatic compound with formaldehyde (for example, JP53-24973 B). Meanwhile, J. Gordon Robinson and co-worker reported their research on the synthesis of aromatic resins by the reaction of naphthalene with formaldehyde in the presence of sulfuric acid (The British Polymer Journal, June, 1980, pp. 61–69) and, for the separation of the sulfuric acid catalyst, they used a large amount of 1,2-dichloroethane and an adequate amount of benzyldimethyldodecylammonium chloride as a surfactant to separate the organic and aqueous layers. This procedure was adopted because of an extreme difficulty of separating the organic and aqueous layers.
It is thus publicly known that the organic layer can be separated from the aqueous layer by the use of a surfactant as a demulsifier in the aforementioned reaction. However, even the addition of a surfactant has faced problems such as contamination of aromatic oligomers recovered from the organic layer due to insufficient separation of the organic and aqueous layers and necessity for use of large quantities of an organic solvent.